The
Arctic is losing its old, thick ice faster than in previous years,
according to satellite data.

The loss
has continued since the end of the Arctic summer, despite cold weather
across the northern hemisphere.

The warm
2007 summer saw the smallest area of ice ever recorded in the region,
and scientists say 2008 could follow a similar pattern.

Older floes
are thicker and less saline than newly-formed ice, meaning they can
survive warm spells better.

Ice more
than two years old now makes up about 30% of all the ice in the Arctic,
down from 60% two decades ago.
The shrinking of Arctic ice has global implications, as its white
surface reflects solar energy back into space whereas the open ocean
absorbs it.

Long
March

March is
the month when the Arctic ice usually reaches its largest extent,
as the dark winter nears its end.

Nasa's
data shows the area covered by ice is roughly the same as it was last
year; but this masks a significant change.

"Although
this March the area is slightly larger than last March, the area of
[thick] perennial ice has reached an all time low," said Seelye
Martin, manager of the Cryospheric Sciences Program at Nasa headquarters
in Washington DC.

"So
the volume of Arctic ice continues to decrease."

The loss of old, thick ice has continued through the winter months,
despite the unusually cold weather deriving from La Nina conditions
(the other extreme of the El Nino Southern Oscillation) in the Pacific.

The winter ice loss is thought to be driven mainly by the transport
of old floes from Arctic waters out into the Atlantic Ocean. The currents
driving this are stronger than usual as a consequence of another natural
cycle, the Arctic Oscillation.

The net
result is that most of the cover consists of ice that has formed since
last summer.

The scientists
behind these findings believe this year's cooling should not obscure
the long term warming trend, with temperatures across the Arctic rising
about twice as fast as the global average.

"Weather
comes and goes, and it's the long term average that really matters,"
observed Josefino Comiso from Nasa's Goddard Space Flight Center.

Dr Comiso
said he believed that the change of albedo - the change from a white,
reflective surface of ice to a dark, absorbing surface of sea - was
already happening.

Summer
sailing

With the
ice pack containing such a high proportion of thin, salty ice, the
scientists believe another major melt is likely in the summer.

"It's
becoming thinner and thinner and much more susceptible to melting
during the summer - much more likely to melt away," commented
Walt Meier from the National Snow and Ice Data Center (NSIDC) in Boulder.

"It
may look OK on the surface, but it's like looking at a Hollywood movie
set - you see the facade of a building and it looks OK, but if you
look behind it, there's no building there."

Last summer,
the sharp melt meant that the Northwest Passage, the fabled navigation
route linking the Atlantic and Pacific Oceans across the top of North
America, was easily navigable.

The disappeance
of ice cover has countries around the Arctic eagerly eyeing the mineral
reserves that may become accessible.

Most projections
of climate change in the Arctic suggest the ocean may become ice-free
by the middle of the century, but one forecast released late last
year said it could happen by 2013.

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